Genes, disc degeneration and weight combine to give lower back pain

Abstract

MedWire News: Lumbar disc degeneration (LDD) is the major contributing cause of nonspecific lower back pain (LBP) in women, say researchers who found the two conditions shared some genetic factors.

Being overweight is also a significant contributing factor to LBP, report Frances Williams (King's College London, UK) and co-workers in the journal Annals of Rheumatic Diseases.

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To investigate contributing factors to LBP unrelated to menstruation, pregnancy or fever, the team examined 2256 women, composed of 371 monozygotic and 698 dizygotic twin pairs, 29 sibling pairs, and 60 singletons, aged an average of 50 years old.

The women were questioned regarding weight, smoking, occupation, and exercise. Magnetic resonance imaging (MRI) was used to grade the five intervertebral discs of the lumbar spine according to disc signal intensity within the nucleus pulposus, disc height, disc extension, and anterior osteophytes. This information was used to create the lumbar spine summary score (LSUM).

Analysis showed that disabling LBP - defined as affecting activities in daily living for more than 1 month ever - was significantly predicted by LSUM, being overweight, partaking in physical exercise, and the presence of LBP in the co-twin.

Specifically, women were 5.8 and 2.2 times more likely to have disabling LBP if their monozygotic or dizygotic co-twin had LBP, respectively. Women in the top 90th centile for weight were 1.9 times more likely to have LBP than those in the bottom 10th.

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All four MRI traits were significant predictors for LBP but the combined LSUM was the strongest significant predictor for the condition. After adjusting for other risk factors, women with advanced LDD (90th centile) were 3.2 times more likely to have LBP than those without.

Interestingly, there was a significant genetic correlation between LBP and LDD indicating that around 11-13% of genetic effects are shared by LDD and LBP, which the researchers say may have "an important implication for future studies."

"It may suggest the existence of common metabolic pathways leading to the manifestation of both phenotypes and thus direct research towards the specific candidate genes, such as those involved in the metabolism and ageing of nucleus pulposus," conclude Williams et al.